1. Field of the Invention
The present invention relates to a recording apparatus (printer) serving as an information output apparatus to be connected to, for example, a computer. Additionally, the present invention relates to a recording apparatus, incorporated in an image formation system such as a copier or facsimile system, for recording data on a recording medium using a means such as a recording head.
2. Description of the Related Art
Recording apparatuses record data by forming record dots on a recording medium. A so-called serial printer has a recording head, a carriage, a carriage motor, a carriage belt, and a recording medium transporting means. The recording head has recording means, which form record dots on a recording medium, arranged with a predetermined pitch between adjoining dots. The carriage has the recording head mounted thereon and moves in a direction of main scanning. The carriage motor is used to drive the carriage. The carriage belt is used to convey drive exerted by the carriage motor to the carriage. The recording medium transporting means transports a recording medium on which data is recorded by the recording head.
In general, for moving the carriage, on which the recording head is mounted, in the direction of main scanning, the endless belt partly engaged with the carriage is laid between a motor pulley and idler pulley put on the axis of rotation of the carriage motor. The motor pulley and idler pulley are placed in the direction of main scanning with a certain distance between them. The endless belt is moved with a driving force exerted by the carriage motor.
A pulse motor or a DC motor with a rotary encoder is used as the carriage motor.
For calculating the position of the recording head on the recording medium during a main scan, for example, driving pulses applied to the carriage motor are used to determine the timing of driving the recording means in the recording head.
FIG. 14 shows an example of driving pulses, wherein a pulse motor is used as the carriage motor. An angle by which the pulse motor rotates responsively to one pulse is determined. A distance by which the carriage moves responsively to one pulse can therefore be set by specifying the diameter of the motor pulley put on the axis of rotation. In this example, the carriage can move a distance covering two dots on the recording medium responsively to one pulse applied to the carriage motor.
A recording signal used to drive the recording means is set so that the recording pulse will be generated twice between generations of the motor driving pulse.
The first recording pulse is generated simultaneously with the motor driving pulse. Generation of the second recording pulse is delayed by a predetermined time from generation of the first recording pulse using a timer incorporated in a control circuit, so that the second recording pulse will be generated between generations of the motor driving pulse.
In other words, the timing of generating the recording pulse is set based on the driving pulse, which is applied to the carriage motor and used to calculate the position of the carriage on the recording medium during a main scan, so that data can be recorded on the recording medium with a uniform distance between adjoining dots.
However, according to the method of determining the timing of recording by driving the carriage using the motor, there are various factors causing irregularity in the moving speed at which the carriage is moved. The irregularity in the moving speed occurs at the same phase in the direction of main scanning on the recording medium. This leads to irregularities in an image formed on the recorded image. Thus, the method has a drawback that should be overcome.
For example, the pulse motor has several phase positions (normally, four phase positions), to which a driving pulse is applied, defined therein. The driving pulse is applied sequentially to the phase positions, whereby a torque is produced.
An irregularity in rotation occurs at regular intervals due to a difference in magnetic force generated with input of the driving pulse to one phase position or a difference in precision of an angle defined by each of the four phase positions and an adjoining one.
In other words, even when the motor driving pulse is input at regular intervals, a lag or lead in an angle of rotation occurs with input of every fourth pulse. This causes the position of the carriage to slightly deviate from an intended position. Recording is repeated in this state. Consequently, a stripe pattern is drawn in a record image on the recording medium.
FIG. 15, FIG. 16, and FIG. 17 show how the stripe pattern is drawn.
FIG. 15 shows a deviation of a dot from a predetermined position occurring when a recording signal is produced by the recording means at a predetermined position ((n/8)xcex) (wavelength xcex=8 dots (associated with four motor driving pulses)). Herein, two dots are formed between applications of the driving pulse to the carriage motor.
xe2x80x9cLEADINGxe2x80x9d indicates that each dot is formed at a position that is located downstream of a predetermined position in the direction of main scanning. xe2x80x9cLAGGINGxe2x80x9d indicates that each dot is formed at a position that is located upstream of a predetermined position in the direction of main scanning.
FIG. 16 shows how the deviation of each dot indicated in FIG. 15 appears actually on the recording medium. A deviation Z(X) of each position X=(n/8)xcex from an ideal position on the recording medium is expressed as follows:
Z(X)=A sin(2xcfx80(X/xcex))
where A denotes an amplitude.
Thus, a coarse array of dots and a dense array of dots are produced at regular intervals. Factors causing this kind of cyclic irregularity include the foregoing irregularity in rotation of the motor as well as the eccentricity of the motor pulley for conveying drive exerted by the carriage motor to the carriage belt.
FIG. 17 shows record dots formed in a certain area on a recording medium. The coarse and dense array of dots indicated in FIG. 16 appear at regular intervals, whereby a stripe pattern is created in the direction of main scanning.
Even when a multi-pass recording method conventionally utilized as a high-image quality mode is adopted, the relationship between the position of the carriage in the direction of main scanning and a position to which the carriage motor is rotated remains unchanged because the endless belt is used to convey drive. Production of the stripe pattern cannot be prevented. Herein, the multi-pass recording method is a recording method of forming every fifth or sixth dot out of one row of dots during one main scan, and main scanning is performed a plurality of times in order to complete an image.
As mentioned above, the conventional method of determining timing of recording by driving the carriage using the motor has a drawback that irregularity in recording occurs in the direction of main scanning.
For overcoming the foregoing drawbacks, a motor capable of rotating by a precise angle may be used as the carriage motor or the precision of the pulley may be improved. However, taking these measures results in an expensive apparatus.
Even inexpensive serial printers are demanded to be able to record high-definition images these days. There is therefore an increasing demand for a technology of overcoming the irregularity in recording observed in the direction of main scanning by adopting an inexpensive means.
For solving the foregoing problems, a recording apparatus in accordance with the present invention includes a carriage, a carriage motor, a transporting mechanism, a signal generating means, and a recording signal control means. The carriage scans a recording medium in a direction of main scanning with a recording head mounted thereon. The recording head has a plurality of recording means for forming record dots on the recording medium arranged therein. The carriage motor drives the carriage. The transporting mechanism transports the recording medium in a direction of sub scanning. The signal generating means generates a position signal, based on which the position of the carriage in the direction of main scanning can be calculated, responsively to a movement in the direction of main scanning made by the carriage. The recording signal control means calculates the position in the direction of main scanning of the recording head according to the position signal, and generates the recording signal with which the recording means is driven. The recording apparatus further includes a control means in which a plurality of kinds of timing, according to which the recording signal is generated after generation of the position signal based on which the position in the direction of main scanning of the carriage can be calculated, is set relative to the position signal. Any of the plurality of kinds of timing is selected in order to control the recording signal during a main scan involving the carriage.
Additionally, a recording apparatus includes a carriage, a carriage motor, a transport mechanism, a signal generating means, and a recording signal control means. The carriage scans a recording medium in a direction of main scanning with a recording head mounted thereon. A plurality of recording means for forming record dots on a recording medium is arranged in the recording head. The carriage motor drives the carriage. The transport mechanism transports the recording medium in a direction of sub scanning. The signal generating means generates a position signal, based on which the position in the direction of main scanning of the carriage can be calculated, responsively to a movement in the direction of main scanning made by the carriage. The recording signal control means calculates the position in the direction of main scanning of the recording head according to the position signal, and generates a recording signal used to drive the recording means. The recording apparatus operates in a mode in which main scanning involving the carriage is repeated a plurality of times in order to form an array of record dots in the direction of main scanning. The recording apparatus further includes a control means in which a plurality of kinds of timing, according to which the recording signal is generated after generation of the position signal based on which the position in the direction of main scanning of the carriage can be calculated, is set relative to the position signal. The control means associates the plurality of different kinds of timing with a plurality of main scans required to complete the array of record dots to be formed in the direction of main scanning.
Furthermore, a recording apparatus includes a carriage, a carriage motor, a transport mechanism, a signal generating means, and a recording signal control means. The carriage scans a recording medium in a direction of main scanning with a recording head mounted thereon. A plurality of recording means for forming record dots on a recording medium is arranged in the recording head. The carriage motor drives the carriage. The transport mechanism transports the recording medium in a direction of sub scanning. The signal generating means generates a position signal, based on which the position in the direction of main scanning of the carriage can be calculated, responsively to a movement in the direction of main scanning made by the carriage. The recording signal control means calculates the position in the direction of main scanning of the recording head according to the position signal, and generates one or a plurality of recording signals used to drive the recording means between generations of the signal. The recording apparatus operates in a mode in which main scanning involving the carriage is repeated in order to form an array of record dots in the direction of main scanning. The recording apparatus further includes a control means in which a plurality of kinds of timing, according to which the recording signal is generated after generation of the position signal based on which the position in the direction of main scanning of the carriage can be calculated, is set relative to the position signal. The control means associates the plurality of different kinds of timing with a plurality of main scans required to complete the array of record dots to be formed in the direction of main scanning.
Moreover, a method of controlling a recording apparatus in accordance with the present invention is implemented in a recording apparatus including a carriage, a carriage motor, a transport mechanism, a signal generating means, and a recording signal control means. The carriage scans a recording medium in a direction of main scanning with a recording head mounted thereon. A plurality of recording means for forming record dots on a recording medium is arranged in the recording head. The carriage motor drives the carriage. The transport mechanism transports the recording medium in a direction of sub scanning. The signal generating means generates a position signal, based on which the position in the direction of main scanning of the carriage can be calculated, responsively to a movement in the direction of main scanning made by the carriage. The recording signal control means calculates the position in the direction of main scanning of the recording head according to the position signal, and generates a recording signal used to drive the recording means. One of a plurality of kinds of timing, according to which the recording signal is generated after generation of the position signal based on which the position in the direction of main scanning of the carriage can be calculated and which is set relative to the signal is selected in order to generate the recording signal during the main scan involving the carriage.
Owing to the foregoing configuration, irregularity in recording appearing as streaks or stripes in the direction of main scanning can be suppressed without a rise in costs. Moreover, excellent record images can be produced with high quality.